Object-Oriented Programming SWE211
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Questions and Answers

What does the File class encapsulate?

The properties of a file or a path.

What type of file is designed to be handled by programs?

Binary files

Text files can be read by the JVM.

False

Which of these classes are a subclass of OutputStream in Java? (Select all that apply)

<p>FilterOutputStream</p> Signup and view all the answers

What is the return type of the read() method in InputStream?

<p>An <code>int</code> that represents a byte.</p> Signup and view all the answers

What is the purpose of FilterInputStream and FilterOutputStream?

<p>To filter bytes for specific purposes.</p> Signup and view all the answers

It is possible to create a FileInputStream with a non-existent file.

<p>False</p> Signup and view all the answers

What might happen if you attempt to create a FileOutputStream with an existing file using the first two constructors?

<p>The existing file will be deleted.</p> Signup and view all the answers

What constructor(s) of FileOutputStream can be used to append data to a file?

<p>The constructors that accept a boolean <code>append</code> parameter and set it to <code>true</code>.</p> Signup and view all the answers

What is the advantage of using DataInputStream and DataOutputStream?

<p>They allow reading and writing primitive data types and strings more conveniently.</p> Signup and view all the answers

What are the primary methods provided by DataInputStream and DataOutputStream for writing primitive data types?

<p>Their primary methods are ones like <code>writeInt()</code>, <code>readDouble()</code>, <code>writeChar()</code>, and <code>writeUTF()</code>. These methods are often used to write and read data from files and streams.</p> Signup and view all the answers

The Serializable interface has methods that must be implemented.

<p>False</p> Signup and view all the answers

What is the role of ObjectInputStream and ObjectOutputStream?

<p>They are used to read and write objects to streams.</p> Signup and view all the answers

All objects can be written to a stream.

<p>False</p> Signup and view all the answers

What is the benefit of implementing the Serializable interface? (Select all that apply)

<p>It allows the JVM to automatically manage the serialization process.</p> Signup and view all the answers

What does the readObject method of ObjectInputStream do?

<p>It reads the data from a stream and recreates an object.</p> Signup and view all the answers

An array is serializable if at least one of its elements are serializable.

<p>False</p> Signup and view all the answers

What is the key difference between sequential files and random access files?

<p>Sequential files can only be read or written in a linear order, while random access files allow reading or writing at any specific location within the file.</p> Signup and view all the answers

The RandomAccessFile class allows for both reading and writing to files.

<p>True</p> Signup and view all the answers

The seek() method in RandomAccessFile moves the file pointer to the beginning of the file.

<p>False</p> Signup and view all the answers

Which of the following methods can be used in RandomAccessFile? (Select all that apply)

<p>writeChars()</p> Signup and view all the answers

Write a method call in RandomAccessFile to create a new file that can be read from and written to.

<p><code>RandomAccessFile raf = new RandomAccessFile(&quot;test.dat&quot;, &quot;rw&quot;);</code></p> Signup and view all the answers

Write a method call in RandomAccessFile to create a new file that only allows reading.

<p><code>RandomAccessFile raf = new RandomAccessFile(&quot;test.dat&quot;, &quot;r&quot;);</code></p> Signup and view all the answers

Study Notes

Object-Oriented Programming SWE211

  • Object-Oriented Programming course, SWE211, is presented.

Java I/O

  • File objects encapsulate file properties but lack data reading/writing methods.
  • Java I/O classes are needed for I/O operations.
  • Scanner and PrintWriter are used to read and write files, example shown using temp.txt.

Text File vs. Binary File

  • Text files store data in human-readable form.
  • Binary files store data in binary format, not readable by humans.
  • Java source code is in text files, while class files are binary files.
  • Binary files are more efficient for processing than text files.
  • Text files composed of characters, binary composed of bits. Decimal 199 is '199' in text file and C7 in binary file (decimal 199 = hex C7).

Binary I/O Classes

  • Java's hierarchy of input/output classes for binary files.

InputStream / OutputStream

  • Values returned/written are bytes as integers

FileInputStream/FileOutputStream

  • Connects input/output streams with external binary files.
  • Methods are inherited from superclasses.

FileInputStream

  • Used for creating input streams to files
  • FileInputStream(String filename)
  • FileInputStream(File file)
  • FileNotFoundException if file doesn't exist.

FileOutputStream

  • FileOutputStream(String filename)
  • FileOutputStream(File file)
  • FileOutputStream(String filename, boolean append)
  • FileOutputStream(File file, boolean append)
    • Creates a new file if it doesn't exist.
    • Deletes existing file content if using the first two constructors.
    • Appends to existing file using the last two.

Example Code (TestFileStream)

  • Demonstrates reading and writing integers to/from a binary file using FileInputStream and FileOutputStream.

FilterInputStream/FilterOutputStream

  • Filter streams modify basic byte input/output streams for various purposes.
  • DataInput and DataOutput filter bytes needed to read integers, doubles, and strings.

DataInputStream/DataOutputStream

  • DataInputStream reads bytes from a stream and converts them into primitive data types or strings.
  • DataOutputStream converts primitive data types or strings into bytes for writing to a stream.

DataInputStream

  • Implements DataInput interface, extending FilterInputStream.
  • Reads primitive data types from a stream.

DataOutputStream

  • Implements DataOutput interface, extending FilterOutputStream.
  • Writes primitive data types or strings to a stream.

Using DataInputStream/DataOutputStream

  • Wrappers to filter data from existing input/output streams for specific data types.
  • Example using DataInputStream and DataOutputStream on in.dat and out.dat.

Concept of Pipe Line

  • Input/output can flow sequentially in a pipe-line fashion.

Order and Format

  • Data must be read in the same order and format that it is written.
  • Using UTF-8 example, data must be read using readUTF.

Checking End of File

  • EOFException occurs if attempting to read past end of stream.
  • input.available() checks if end of file is reached.

Example Demonstrating File Handling

  • Demonstrates various I/O related functions

BufferedInputStream/BufferedOutputStream

  • Use buffers to improve I/O speed (memory areas to temporarily hold data)

Constructing BufferedInputStream/BufferedOutputStream

  • Java methods used to create buffered input/output streams.

Object I/O

  • Enables file input/output for primitive types values and strings (using DataInputStream/DataOutputStream) and also for objects.

Using Object Streams

  • You wrap ObjectInputStream or ObjectOutputStream using constructors ObjectInputStream(InputStream in) and ObjectOutputStream(OutputStream out)

Example of object handling (example program)

  • Example saving object data to foo.bin file, demonstrates ObjectOutputStream

The Serializable Interface

  • Enables Java's serialization mechanism for object and array handling.
  • Java will assign a serial number to each object, and use this to re-create it later.

Example Using Foo class

  • Saving objectFoo instances to the file foo.bin Using object output stream, writeObject(object).

Reading Objects

  • Reading back instances/objects using readObject.

Serializing Arrays

  • Entire arrays can be serialized if all elements are serializable.

Random Access Files

  • Stream data that can be read and written to at random positions in a file.

RandomAccessFile Methods

  • Methods (similar to DataInputStream and DataOutputStream) handle random file access.

RandomAccessFile Constructor

  • Demonstrates RandomAccessFile class constructors for "read/write" or "read only" mode.

Sample Code (RandomAccessFile)

  • Demonstrates various random access file operations
  • Methods to retrieve and modify data at specific byte positions.

Practice

  • Exercises and coding practice
  • Code presented to read/extract text & file content

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Related Documents

SWE211 - Lect08 - Binary files PDF

Description

This quiz covers Object-Oriented Programming concepts as presented in the SWE211 course. Topics include Java I/O operations, distinctions between text and binary files, and the Java input/output class hierarchy. Test your understanding of file reading/writing processes and their efficiency.

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